Siding Square Calculator
Siding is sold by the "square" — one square covers 100 square feet of wall. Enter your total net wall area (after subtracting windows and doors) plus a waste allowance, and this calculator tells you how many squares to order so you don't come up short mid-job.
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Your results
Estimate only — subtract windows and doors from the wall area first, or the result runs high.
How to use this calculator
Measure each exterior wall (height × width), add the totals together, then subtract the area of every window, door, and garage opening. Enter that net figure as your wall area.
Pick a waste allowance: 10% is the standard for simple rectangular walls, while gables, dormers, bay windows, and lots of corner cuts call for 15%. The calculator adds the waste and rounds the order up to whole squares — you can't buy a fraction of a square.
How it works
The math is simple division and rounding: net squares = wall area ÷ 100, then squares to order = round-up(net squares × (1 + waste%)). One square is exactly 100 square feet of coverage, so 320 sq ft gives 3.2 squares, and a 10% waste factor pushes that to 3.52 — rounded up to 4 squares to order.
This is a material-planning estimate, not a cut diagram. Trim and accessories — corner posts, J-channel, starter strips, soffit — are counted separately and are not included here.
Frequently asked questions
What is a square of siding?
One square covers 100 square feet of wall — the industry unit for ordering siding.
Should I subtract windows and doors?
Yes. Measure gross wall area, then subtract openings for an accurate material count.
How much waste should I add?
10% is typical for straight walls; use 15% for gables, dormers, and lots of cuts.
Does this include trim and accessories?
No — corner posts, J-channel, and starter strips are estimated separately.